I may be able to help here.
Though firmer chisels would not be suitable in their current state (short handles, etc. I have done this myself in working out some tool designs in the past.
Here's the trick. Some obvious, some not so.
First, let's consider the size of the handles. short handles will not help with firmer chisels for turning as the point of balance and weight distribution would not work. The best thing is to have someone make you some 15" handles to a normal turning tool profile with the ferrules.
The blade itself. Though it's not suitable for roughing gouges, etc, you can create reasonable scraper type tools which can rough to a degree but don't expect the forces you can generate out of a normal spindle gouge in terms of rough cutting and deep cutting.
The trick is firstly to consider the grind and shape of the tool. the traditional grind of a firmer chisel is too aggressive and would not support the cut for a spinning piece. so a lesser grind is best. 30deg or les would do.
the shape can remain as a square edge, full round, dome, right or left hand or V scrape, though it is worth noting that a V scrape will need a lesser angle and also a relief angle at both sides of the "V" profile.
The issue here is grinding the profile and changing the temper of the steel. It's always best to take your time and not present force to the blade you wish to sharpen in the hope of removing more stock. what you effectively do is create a weak spot with the heat generated from the stone of a bench or angle grinder.
the solution is a small pot of oil as a dipping component, this creates two advantages. Stabilising the temper and also giving an easier grind. Don't ex[ect the grinder to perform large amounts of waste removal. just let it take it's time.
The finish of the blade is important. polishing the sides and underside help with the toolrest, so the use of a lapping plate and fine grade abrasives will help.
The top face can either be left in it's current state or with a bit of care and time, the use of a grinder to lightly impart a scoop channel along the blade as a chip clearance profile would benefit you. again the use of oil dipping to cool the surface is important, as is the use of the grinder to achieve the finish. Again, don't apply pressure to remove large quantities of stock from the steel as this WILL effect the stability of of the temper.
Aside from this, I can offer a more effective solution if you can gain access to a toolmaker or steels supplier.. You could try toolmaking from the old approach I follow where fresh solid steel (rockwell 55-65 or in those lines) either as flat stock (square / rectangular) or round solid steel can be ground and shaped. You can get away to a degree with heavier strokes for grinding. steels like HSS or HSS-M2, HCS (high carbon steel) and the likes of will be good starting points. HCS is easier to shape but requires more grinding and honing as time goes on, so it's not always the best option depending on the quality.
anyway, hope it can help a bit
